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Ann Thorac Surg 2000;70:778-783
© 2000 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Influence of concomitant CABG and urgent/emergent status on mitral valve replacement surgery

^a Division of Cardiothoracic Surgery, Carlyle Fraser Heart Center, Department of Surgery, Atlanta, Georgia, USA
^b Emory Center of Outcomes Research, Atlanta, Georgia, USA
^c Division of Cardiology, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, USA

Address reprint requests to Dr. Guyton, The Emory Clinic, 1365 Clifton Rd, Atlanta, GA 30322
e-mail: rguyton{at}emory.edu

Presented at the Forty-sixth Annual Meeting of the Southern Thoracic Surgical Association, San Juan, Puerto Rico, November 4–6, 1999.

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. Outcomes and resource utilization of patients undergoing mitral valve replacement (MVR) with or without concomitant coronary artery bypass grafting (CABG) were reviewed.

Methods. Data for 1,844 patients undergoing isolated primary MVR at Emory University Hospitals between 1980 and 1997 were recorded prospectively in a computerized database.

Results. The four groups included patients undergoing elective MVR with (n = 360) or without CABG (n = 1332) and urgent/emergent MVR with (n = 66) or without CABG (n = 86). Length of stay was significantly higher in patients undergoing elective MVR with CABG (15 days) than in those without CABG (11 days) but was not significantly different in patients undergoing urgent/emergent MVR with CABG (17 days) than in those without CABG (19 days). In-hospital mortality was significantly higher for patients undergoing elective (14%) or urgent/emergent (41%) MVR with CABG than in those undergoing MVR without CABG (elective:6%; urgent/emergent:20%). The 19-year survival rate was 32% for patients undergoing elective MVR with CABG compared with 51% for those without CABG and 28% for patients undergoing urgent/emergent MVR with CABG compared with 46% for those without CABG. Multivariate correlates of long-term mortality included older age, concomitant CABG, and urgent/emergent status. Hospital costs were significantly higher for patients undergoing elective MVR with ($33,216) than for those without ($23,890) CABG. No significant difference in cost were noted between patients undergoing urgent/emergent MVR with ($40,535) and without ($31,981) CABG.

Conclusions. The addition of CABG or urgent/emergent status to patients undergoing MVR significantly increases morbidity, mortality, and costs. Careful scrutiny of the benefits versus resource utilization is required for patients undergoing high risk MVR.

	Introduction

Top Abstract Introduction Material and methods Results Comment References

 
Despite the recent technologic advances in critical care and surgical techniques, morbidity and mortality for some patients undergoing isolated mitral valve replacement (MVR) remains considerable [1–3]. We [3] and others [4] have shown that, although the trends for patients undergoing mitral valve surgery have reflected an increase in mean age and associated comorbid risk factors, the morbidity and mortality for these patients have remained relatively constant. In one series, although the incidence of concurrent coronary artery bypass grafting (CABG) with mitral valve replacement increased significantly from 1988 (18%) to 1997 (28%); the in-hospital survival rates for the same two periods were similar (89% versus 90%, respectively) [3]. Clearly, concomitant coronary artery bypass grafting in patients undergoing primary mitral valve replacement has been shown to be an important independent risk factor for short- and long-term mortality [5–7]. However, data for short- and long-term mortality in patients undergoing elective versus urgent/emergent concomitant CABG and MVR have been lacking.

Similarly, urgent/emergent mitral valve replacement surgery has been shown to be significant independent predictor of survival [7]. Although clinical series have reported overall morbidity and mortality rates associated with MVR, reports delineating the long-term follow-up and resource utilization of elective versus urgent/emergent MVR with the confounding factor of CABG are lacking. Therefore, the purpose of the current study was to compare short- and long-term survival and resource utilization within a large cohort of patients undergoing elective or urgent/emergent mitral valve replacement with or without concomitant coronary artery bypass grafting at Emory University Hospitals.

	Material and methods

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We found that 1,844 consecutive patients underwent primary mitral valve replacement at Emory University Hospitals from 1980 to 1997. Over the 17-year period, elective mitral valve replacement was performed in 1,692 patients (92%). Of this elective population, mitral valve replacement without concomitant CABG was performed in 1,332 patients and mitral valve replacement with concomitant CABG in 360 patients. From 1980 to 1997, urgent or emergent isolated primary mitral valve replacement was performed in 152 patients (8%). Eighty-six patients underwent urgent or emergent MVR without CABG, while 66 patients had concomitant MVR and CABG. Patients who underwent mitral valve repair during the present study were not included in that figure. Clinical and procedural data were recorded prospectively on standardized forms by trained medical personnel and entered into a computerized database. All fields were defined in a data dictionary.

Standard cardiopulmonary bypass techniques were used for all patients undergoing mitral valve replacement surgery. Generally, myocardial protection was achieved with systemic hypothermia and ischemic arrest with cold blood antegrade and retrograde potassium cardioplegia and topical hypothermia and aortic occlusion in all patients. Specific extracorporeal circulation and myocardial protection strategies were implemented as per the attending surgeon. When possible, posterior valve chordal preservation was performed.

Definitions for variables studied include the following: urgent procedure, a procedure judged by the attending cardiac surgeon to be required within 24 hours from presentation; emergent procedure, a procedure performed in the setting of acute ischemia, infarction, or hemodynamic compromise; postoperative myocardial infarction, development of significant new Q waves on electrocardiogram; discharged alive, includes in-hospital mortality for all patients, whether or not patients received concomitant CABG; related variables, defined from the patient’s history and physical examination, included hypertension, diabetes mellitus, severity of angina, and previous myocardial infarction. The Canadian Cardiovascular Society (CCS) Classification was used to define the severity of angina and the New York Heart Association criteria (The Criteria Committee) to define severity of congestive heart failure.

Follow-up information was obtained from direct communication (telephone or letter) with the patient, family, attending physicians, or a combination of these. Additional information on patients who had died was obtained from the state bureau of records. Patients not readmitted to Emory University Hospitals were contacted by telephone or letter. Follow-up data were available for 1,719 of the 1,844 patients (93%). All follow-up information was recorded on standardized forms and entered into a computerized database.

Hospital charges were obtained from the UB92 formulation of the hospital bill provided by the hospital finance department. Charges were reduced to costs using departmental cost to charge ratios obtained from the hospital cost report, which is provided to the Health Care Financing Agency yearly. All costs were inflated to 1997 costs using the Medicare cost inflation rate. The clinical and financial data were combined in a single computerized database with the patients’ social security numbers as the primary key.

Statistical analysis
The data are expressed as proportions or as the mean ± standard deviation. Differences in categorical variables were analyzed by ² analysis (or Fisher’s exact test), and differences in continuous variables were analyzed by Student t tests. Overall survival (cardiac and noncardiac related deaths) were determined by the Kaplan-Meier method; the estimated probability is shown together with the standard deviation. Multivariate correlates of survival were determined by Cox model analysis; variables that were frequently missing were eliminated to determine the impact of missing data on the analyses. Goodness-of-fit of the final models was examined using the adjusted c index. Statistical modeling and testing were performed using S-PLUS statistical software (MathSoft, Cambridge, MA). Results were considered significant if p values were less than 0.05.

	Results

Top Abstract Introduction Material and methods Results Comment References

 
Effects of concomitant coronary artery bypass grafting
The demographics and medical history of patients undergoing mitral valve surgery at Emory University Hospitals form 1980 to 1997 are described in Table 1. The patients undergoing elective concomitant coronary bypass and MVR were significantly older, were more often male and were more likely to have hypertension, CCS class III to IV angina, and a prior myocardial infarction than were those patients undergoing elective MVR without CABG (Table 1). Similarly, patients undergoing urgent/emergent concomitant coronary bypass and MVR were significantly older, more often male, and more likely to have hypertension, class III to IV angina, and a previous myocardial infarction than were those patients with urgent/emergent MVR without CABG (Table 1).

In-hospital outcomes including the occurrence of postoperative stroke and in-hospital mortality were significantly more common in those patients undergoing urgent/emergent mitral valve replacement without concomitant coronary artery bypass grafting than in those patients undergoing elective MVR without concomitant coronary bypass (Table 2). Length of stay and hospital cost were also significantly increased in patients undergoing urgent/emergent MVR without concomitant CABG (Table 2). In contrast, only in-hospital mortality was significantly higher in patients undergoing urgent/emergent MVR with CABG, than in those undergoing elective MVR with CABG (Table 2).

Predictors of mortality
Multivariate correlates of in-hospital mortality are shown for the total population in Table 3. Older age, concomitant CABG, and procedure status were correlates for in-hospital mortality in the total population. Urgent/emergent status was the most important predictor of in-hospital mortality, as indicated by the highest odds ratio (OR 4.37). No significant interaction term was found between concomitant CABG and urgent/emergent status; thus, urgent/emergent status was similarly predictive of outcome in patients with and without CABG, and CABG was similarly predictive of outcome in elective versus urgent/emergent patients.

View larger version (32K): [in this window] [in a new window]   Fig 1. Survival for the entire population of patients undergoing primary isolated mitral valve replacement at Emory University Hospitals from 1980 to 1997. Group 1 = elective mitral valve replacement without concomitant coronary artery bypass surgery, group 2 = urgent/emergent mitral valve replacement without concomitant coronary artery bypass surgery, group 3 = elective mitral valve replacement with concomitant coronary artery bypass surgery, and group 4 = urgent/emergent mitral valve replacement with concomitant coronary artery bypass surgery.

	Comment

Top Abstract Introduction Material and methods Results Comment References

Patients undergoing urgent/emergent MVR with CABG had significantly higher incidence of CCS class III to IV angina and history of a previous myocardial infarction (Table 1) than did those patients undergoing elective MVR with CABG. However, in the current series no significant differences were noted in the incidence of postoperative myocardial infarction or stroke in patients undergoing elective or urgent/emergent NVR with concomitant CABG (Table 2). Andrade and colleagues [8] report that the need for emergency operation increases the in-hospital mortality rate from 8% to 39% in patients undergoing MVR with concurrent CABG. Similarly, we report an increase in in-hospital mortality rate from 14% in elective patients undergoing MVR with CABG to 41% in urgent/emergent patients undergoing MVR with CABG. Once again, the profound differences in early mortality between these groups decreased over time, such that at ten years, survival is similar between patients undergoing elective MVR with CABG and urgent/emergent MVR with CABG (Fig 1).

Interestingly, a lack of interaction of status and CABG was found among patients undergoing mitral valve replacement. Although the worst outcome overall was found in the urgent/emergent MVR with CABG group, there was little interaction with the status. Thus, the effect of CABG in the urgent/emergent MVR group was similar to that in the elective MVR group. Overall, urgent/emergent surgical status in the present study was the most important multivariate predictor for in-hospital mortality (odd ratio, 4.37). The effects of urgent/emergent status on patients undergoing MVR with or without CABG was less pronounced as a multivariate predictor for long-term mortality (odds ratio, 1.40).

We have previously shown that the proportion of our patients undergoing mitral valve replacement with catheterization-proven coronary artery disease increased significantly (30% of our population in 1988% to 43% in 1997, p = 0.002), as did the proportion of patients who underwent MVR with concurrent CABG (18% in 1988% to 28% in 1997, p = 0.0003) [3]. Comparing patients undergoing elective MVR with CABG with those without concomitant CABG, the first group was overall were sicker, were older, and had a higher incidence of hypertension, class III to IV angina, and history of a previous myocardial infarction (Table1). As expected, outcomes for patients undergoing elective MVR with CABG had a significantly higher incidence of postoperative myocardial infarction and stroke (Table 2). Similarly, patients undergoing urgent/emergent MVR with CABG were sicker than patients undergoing urgent/emergent MVR without CABG. However, the difference between the two groups in incidence of postoperative myocardial infarction and stroke was not statistically significantly.

Various studies have reported the profound effect of coronary artery disease on perioperative survival after mitral valve replacement [9–11]. Increases in the incidence of significant coronary artery disease leading to MVR combined with CABG has a significant impact on the eventual patient outcome, so that in-hospital mortality rates for these high risk patients may range from 7% to 24% [12–14] In the present study, the in-hospital mortality rate for patients undergoing elective MVR with CABG was 14%—significantly higher than the in-hospital mortality rate of 6% for patients undergoing elective MVR without CABG. Various investigators have reported that the independent predictors for in-hospital mortality for patients undergoing MVR with CABG include age greater than 60 years, NYHA Class IV, previous history of myocardial infarction or congestive heart failure, more than three coronary grafts, emergency operation, cardiac enlargement, and decreased left ventricular ejection fraction [5, 8]. In the present study, the second most important multivariate predictor for in-hospital mortality in patients undergoing mitral valve replacement was concomitant CABG (OR 2.06).

Correspondingly, long-term follow-up in patients undergoing MVR with CABG found higher mortality rates in that group than in patients undergoing MVR without CABG. Lytle and colleagues [12] and others [13, 15] have reported an approximately 30% to 50% 10-year actuarial survival rate for patients who undergo combined MVR and coronary revascularization, compared with a similar survival rate of approximately 60% for MVR without coronary revascularization. However, these results represent the overall survival, irrespective of the surgical status (elective versus urgent/emergent). Surprisingly, in the present study, there was not a large difference in the 10-year survival rate of urgent/emergent patients undergoing MVR without CABG (46%) compared with the rate in those patients undergoing elective MVR without CABG group (51%). Similarly, the 10-year survival rate in the urgent/emergent patients undergoing MVR with CABG (28%) was not significantly different from that in the elective MVR with CABG group (32%). Despite the status of patients undergoing MVR, the addition of coronary artery bypass grafting in our series was found to be the second most important multivariate predictor for long-term mortality in patients undergoing mitral valve replacement (OR 1.44).

Although numerous authors have reported on physiologic and short- and long-term results following mitral valve replacement surgery, research evaluating the economic implications of mitral valve surgery is lacking. In the present study, we outline the cost per patient within the subcategories of mitral valve replacement. Although the cost data may be imperfect, because they are derived from estimated cost-to-charge ratios, these values should be valid for internal organizational comparison over time. In patients undergoing MVR without CABG, the performance of the operation on an urgent/emergent basis significantly increases the hospital cost and overall resource utilization, compared with the cost in patients undergoing elective MVR without CABG. Interestingly, in MVR with CABG patients, the cost of elective versus urgent/emergent status is not statistically different. Correspondingly, the resource utilization (length of stay) is also not significantly increased in urgent/emergent MVR with CABG patients compared with elective MVR with CABG patients. For patients undergoing elective MVR surgery, the addition of coronary artery bypass surgery does significantly increase the resource utilization, leading to a significant increase in hospital cost.

In conclusion, patients undergoing CABG with elective or urgent/emergent MVR have increased morbidity, mortality, and in-hospital costs compared with those undergoing MVR without CABG. Furthermore, urgent/emergent MVR status produces significantly increased morbidity, mortality, and costs compared with elective MVR status. Careful preoperative scrutiny of benefit versus resource utilization along with proper conveyance of realistic survival expectations to the patient and his or her family are required for individuals undergoing mitral valve surgery.

	References

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